The present invention relates to a system for making an annular workpiece. More particularly this invention concerns a method of and apparatus for forming a flange.
It is frequently necessary to form an integral flange on a tubular or solid workpiece. For instance a motor-vehicle drive shaft or rear end housing has flanges that allow attachment to a wheel or transmission housing. Such parts must be produced in large quantities to high tolerance, and in view of the application must also be made at the lowest possible unit cost.
As a result the piece is made by forming, normally in a complex multistage operation. The workpiece blank, for example a short length of a tube or rod, is cut off a longer workpiece and then while still warm is fed to the actual forming apparatus. The forming is done in several steps to produce a finished workpiece that in theory needs little or no machining.
Such a process is normal quite difficult and entails considerable handling of the workpiece. It is necessary to treat the workpiece before and after forming e.g. by phosphating after forming to prepare it for a subsequent heat treatment. Furthermore the several different forming steps often lead to misalignment at at least one stage, creating eccentric deformations that render the workpiece unusable.
In standard cold-forming systems the maximum angle of about 2xc2x0 requires relatively high forces to work, and only certain shapes can be made. Furthermore the cycling time is relatively high and loading and unloading the machine, in particular when the workpiece is fairly long, is quite difficult.
Even the system of described in U.S. Pat. No. 5,945,959 which can use an angle up to 10xc2x0 requires the workpiece to be heated, which further complicates use of the system and makes treatment time very critical. Such hot-forming requires the workpiece to be at a forging temperature, which means that it will need to be descaled after treatment. Even though less force can be used to achieve the desired deformation at high temperatures, the advantage is outweighed by the problems of heating and subsequently treating the workpiece. Furthermore when a thin-walled workpiece, e.g. a tube, is being treated it must be deformed rapidly before it cools and becomes too hard to work.
In some systems the end of the workpiece alone is heated electrically, thereby allowing the lower hot-forming pressure to be used. Nonetheless getting the temperature right and deforming while the workpiece maintains the right temperature is difficult, and the overall treatment time is normally quite long.
It is therefore an object of the present invention to provide an improved flanging system.
Another object is the provision of such an improved flanging system which overcomes the above-given disadvantages, that is which produces flanges, either on the end or middle of a workpiece or all alone as a sort of ring, in a simpler manner than the prior art.
More particularly this invention is a method and apparatus for forming a flange on a workpiece which does the entire formation in a single step with the workpiece at a single location.
A flange is formed on a workpiece by first mounting the workpiece in an inner holder shiftable along about a main axis and securing the inner holder against rotation about the main axis. A roller is rotated about the main axis adjacent the inner holder. Then the inner holder and workpiece are displaced axially to press the workpiece axially against the roller and deform the workpiece and form a flange thereon. This is done without heating the workpiece, that is in a cold-forming operation, so that the timing is not important and a very strong and smooth finished product is produced. A high-pressure water cutter can be used to produce the workpieces, so that the starting workpiece is not deformed and can be formed accurately.
It is possible with this system to operate within tolerances of about 0.1 mm. A subsequent machining operation can therefore be eliminated. Furthermore the use of an inner tool, which moves only axially and which can have an axially through-going passage to which the workpiece is fitted, means relatively long workpieces can be flanged relatively easily, since they are not rotated during the flanging operation so that getting them perfectly centered is not important and their mass is largely irrelevant. The cold-forming system of this invention can be used to make relatively thick flanges. Furthermore since it is the outer tool, not the workpiece, that is rotated, it is possible to operate at higher speeds with, therefore, less axial force and a more compact and easily controlled machine.
According to the invention the inner holder is formed around the workpiece with a recess and the workpiece is deformed into the recess. Furthermore a coolant and/or lubricant can be sprayed on the workpiece during deformation of the workpiece.
In accordance with the invention the workpiece is tubular and centered on the main axis. A mandrel is fitted snugly inside the workpiece during deformation of the workpiece. As the flange is formed the mandrel retracts axially against a spring force as the roller deforms the workpiece. In fact during the flanging operation the mandrel engages axially directly against the roller.
It is possible to internally engage the workpiece when it is tubular. Such internal engagement is easiest to do as the workpieces are cut off a longer blank and prevents rolling errors from being a problem. The workpiece can be engaged internally over about half of the wall thickness of the tubular workpiece.
The workpiece according to the invention has ends, one of which projects from the inner holder, and the flange is formed offset from the one end. In this case it is possible to roll down and reduce a wall thickness of the workpiece between the flange and the one end after forming the flange. It is also within the scope of this invention to deform the flange radially inward during deformation by the roller.
The roller according to the invention is rotated about an axis forming an angle of at least 10xc2x0 with the main axis. In addition the roller is prevented from moving axially during the flange-forming operation.
The apparatus for forming a flange on a workpiece thus has according to the invention a frame, an inner holder shiftable on the frame along a main axis and adapted to hold the workpiece, and a roller rotatable about the main axis on the frame adjacent the inner holder. Actuators displace the inner holder and workpiece axially relative to the frame while the inner holder is secured against rotation. This presses the workpiece axially against the roller, deforms the workpiece, and forms a flange on the workpiece.
According to the invention a contactless measuring system connected to the inner holder produces an output usable by a control system to operate the actuators that advance the inner holder and workpiece. The actuators include a pair of double-acting cylinders flanking the main axis and connected between the inner holder and the frame. Such actuators therefore serve not only to advance the inner holder and workpiece against the rollers, but also to retract them therefrom after the flange is formed.
The flange-forming apparatus further has according to the invention a shaft journaled in the frame for rotation about the main axis, connected to the means, and carrying the roller. This shaft can be tubular to allow the inside of a tubular workpiece also to be given a shape by passing an appropriate tool through the tubular shaft. The roller is rotatable on the shaft about a roller axis forming an angle of at least 10xc2x0 with the main axis. In addition a counterweight is provided on the shaft angularly equispaced about the main axis with the roller.
A traverse is axially displaceable on the frame and is fixed axially to a feed shaft displaceable into and out of contact with an inner end of the workpiece in the inner tool. Another actuator is braced between the traverse and the frame for axially displacing the feed shaft. This feed shaft is a tube shaft and a mandrel is slidable along the main axis in the tube shaft. A spring braced against the mandrel urges it axially outward toward the outer tool. During the flanging operation the mandrel actually contacts the roller to prevent the workpiece from collapsing inward.
An outer tool holder can carry a plurality of the rollers angularly equispaced about the main axis. In addition a plurality of secondary rollers carried on the outer tool holder can engage radially inward of the main axis with the flange is formed on the workpiece.